My clerk at the pet store where I buy very expensive cat food told me why cats bring in dead, dying or still kicking creatures, mostly smaller and mostly with feathers. Are you ready for this? Apparently, they are trying to teach us how to kill. They never see us drag in a dead deer so how can we possibly know how to procure food. We can open cans and shake out bags of kibble into their bowls. But we are woefully inadequate in the killing department. So they're showing us how, like they show their kittens.
Aw, wasn't that heartwarming?